This is from Asterius topic:
This means that there can be only a Burn or Corrosive Burn an opponent, but not both at the same time.
Unfortunately I do not had Asterius when this Russell is in Beta so I could not try this out.
I am not sure other Beta Testers have tested it or not.
Maybe someone with Costume Azlar and Asterius can test ithat out if an opponent can have two burns at the same time or not.